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Cisco IOS Cookbook, 2nd Edition by Ian Brown, Kevin Dooley

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Tuning Router Buffers

Problem

You want to change your default buffer allocations to improve router efficiency.

Solution

The router maintains two different sets of buffers: public buffers and interface buffers. The router uses these as temporary storage while processing packet data. You can tune the public buffer pools as follows:

Router1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router1(config)#buffers big initial 100
Router1(config)#buffers big max-free 200
Router1(config)#buffers big min-free 50
Router1(config)#buffers big permanent 50
Router1(config)#end
Router1#

And you can adjust the interface buffer pools by using a similar set of commands:

Router1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
Router1(config)#buffers Ethernet0 initial 200
Router1(config)#buffers Ethernet0 max-free 300
Router1(config)#buffers Ethernet0 min-free 50
Router1(config)#buffers Ethernet0 permanent 50
Router1(config)#end
Router1#

Discussion

Before we start this discussion, we need to offer three notes of caution on tuning buffers. First, adjusting your router’s buffers is usually not necessary. Second, a poor set of buffer parameters can cause serious performance problems on your router and for traffic passing through the router. Third, if you do find that you need to adjust these parameters, the necessary adjustments will be unique to your network, and perhaps even to each router, so we unfortunately can only offer general guidance, but ...

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